This invention relates to an asphalt modifier comprising an emulsion of styrene-butadiene-styrene block copolymer and a styrene-butadiene latex and more particularly, to the asphalt modifier which has an excellent resistance property against plastic deformation, while preventing the occurrence of crack at low temperature.
Ascone, which has been widely used as a road-paving material, is a mixture of both asphalt cement and aggregate. Since it is prepared by heating the mixture, ascone is called as xe2x80x9chot mix asphaltxe2x80x9d or xe2x80x9casphalt binderxe2x80x9d due to the fact that an asphalt cement is combined to aggregate.
Since the roads paved by the asphalt have suffered from frequent ruptures, plastic deformations and detachments under various adverse conditions such as passing of heavy vehicles, weather and traffic environments, the life of roads is getting shorter. Especially, the plastic deformation is the most serious problem that the asphalt-paved roads have encountered. That is, the roads encountered frequently with heavy vehicles will lose their intrinsic functions due to the occurrence of plastic deformation during summer season. Moreover, the outer temperature condition, heavy traffic, and the recent trends toward more heavy and large vehicles make the serious plastic deformation worse.
Under such circumstances, there is urgent need for the development of novel high-quality paving materials and thus the inventor et al. intended to improve the resistance against plastic deformation using the emulsion of styrene-butadiene-styrene block copolymer as asphalt modifier.
However, a single use of the emulsified styrene-butadiene-styrene block copolymer as asphalt modifier was found to effectively prevent the plastic deformation, but the occurrence of crack at low temperature was inevitable due to its resin properties (hardness).
To free from the above shortcomings, the inventor et al. have made intensive studies and noted that the use of both the emulsion of styrene-butadiene-styrene block copolymer and styrene-butadiene latex as asphalt modifier can ensure an excellent resistance property against plastic deformation, while preventing the occurrence of crack at low temperature.
Therefore, an object of this invention is to provide an asphalt modifier which has an excellent resistance property against plastic deformation, while preventing the occurrence of crack at low temperature.
To achieve the above objective, this invention is characterized by an asphalt modifier comprising 5xcx9c30 wt. % of emulsified styrene-butadiene -styrene block copolymer and 7xcx9c95 wt. % of styrene-butadiene latex.
This invention is explained in more detail as set forth hereunder.
In general, the styrene-butadiene-styrene block copolymer generates a lot of cracks at low temperature due to its resin properties. Furthermore, a sigle use of the block copolymer as asphalt modifier will make the production cost high.
Since the elongation property of a styrene-butadiene latex is high at low temperature, its mixture with the emulsion of styrene-butadiene-styrene block copolymer can ensure the prevention of crack at low temperature, while curtailing the production cost with the addition of styrene-butadiene latex in a larger amount.
If the content of the styrene-butadiene latex exceeds 95 wt. % to the total chemical composition of asphalt modifier, the plastic deformation cannot be prevented. On the other hand, if its content is less than 70 wt. %, the inhibitory action against the occurrence of crack at low temperature is minimal with little economical effect. Therefore, it is preferred that 70xcx9c95 wt. % of the styrene-butadiene latex should be added to the total chemical composition of asphalt modifier.
The asphalt modifier of this invention can be selected from the emulsion of styrene-butadiene-styrene block copolymer prepared by the conventional method.
The inventor et al. proposed a method of emulsified the styrene-butadiene-styrene block copolymer, wherein it comprises the following steps of:
solubilizing the styrene-butadiene-styrene block copolymer in a nonpolar solvent to make a solution with the concentration of 10xcx9c15%;
emulsifying 100 wt. parts of the solution in 5xcx9c10 wt. parts of a co-emulsifier and water; and
preparing an emulsion with a certain amount of solid content after the nonpolar solvent is removed using a vacuum equipment and concentrated.
The emulsified styrene-butadiene-styrene block copolymer is mixed with styrene-butadiene latex in order to prepare an asphalt modifier of this invention. The asphalt modifier comprising 5xcx9c30 wt. % of emulsified styrene-butadiene-styrene block copolymer and 70xcx9c95 wt. % of styrene-butadiene latex.
As proposed earlier, the styrene-butadiene latex is prepared comprising the steps of:
a synthesis of seed particle conducted 4xc2x0 C. for 3 hours using 10xcx9c30 wt. parts of butadiene monomer, 3xcx9c10 wt. parts of butylacrylate monomer, 3xcx9c10 wt. parts of styrene monomer, 0.1xcx9c1.0 wt. parts of SLS/0.1xcx9c1.5 wt. parts of rosin salt/0.1xcx9c1.5 wt. parts of fatty salt as emulsifer, 0.1xcx9c1.0 wt. parts of phosphate as electrolyte, 0.2xcx9c1.0 wt. parts of tertiary dodecyl mercaptane as molecular weight modulator, 0.1xcx9c1.0 wt. parts of diisopropylbenzene hydroperoxide as oxidant and 0xcx9c0.5 wt. parts of tetrasodium ethylene diamine tetraacetate hydride as catalyst; and;
an additional polymerization to enlarge the seed particle conducted using 40xcx9c60 wt. parts of butadiene monomer, 3xcx9c13 wt. parts of metylmethaacrylate, 5xcx9c25 wt. parts of styrene monomer, 0.1-2.0 wt. parts of rosin salt as emulsifer, 0.2xcx9c1.0 wt. parts of tertiary dodecyl mercaptane as molecular weight modulator and then, the mixture was reacted for 5 hours by increasing the temperature up to 12xc2x0 C., reacted additionally at 20xc2x0 C. for 5 hours. The temperature was raised at 25xc2x0 C. for the further activation before the termination of the reaction,.
This invention is explained based on the following examples but is not limited by these examples.
The method of emulsified the styrene-butadiene-styrene block copolymer according to the invention is prepared as proposed earlier as follows:
The styrene-butadiene-styrene block copolymer according to this invention is prepared by ourselves; its form includes pellet or powder with the following parameters: styrene content (31%), solution viscosity (15,000 cps), specific gravity (0.94 g/cm3), tensile strength 160 kgf/cm2, 300% tensile stress (28 kgf/cm2) and elongation rate (680%).
First, the styrene-butadiene-styrene block copolymer was dissolved in n-hexane to make its concentration 10xcx9c15%.
Then, 100 wt. parts of the styrene-butadiene-styrene block copolymer solution dissolved in n-hexane were emulsified in the mixture of 5xcx9c10 wt. parts of a co-emulsifier and 80xcx9c100 wt. parts of water. According to this invention. A mixture of rosin salt, fatty salt and oleate was employed as a co-emulsifier.
The styrene-butadiene-styrene block copolymer in n-hexane, which was emulsified by the co-emulsifier, was concentrated to obtain the emulsion of styrene-butadiene-styrene block copolymer. The general description was shown in the following table 1.
To form the initial seed particle during the initial polymerization, all reagents, which were shown in the following table 2 were added to a 2L high-pressure reactor except for diisopropylbenzene hydroperoxide as oxidant and stirred at 3xc2x0 C. for 1 hour. With the addition of diisopropylbenzene hydroperoxide, the polymerization was initiated by increasing the temperature up to 5xc2x0 C.
When the conversion rate of initial monomers reached more than 80% and the initial particle size was grown up to 300 xc3x85 the monomers for the increament were added continuously for the enlargement of particle size and further reaction.
1.0 wt. parts of rosin salt as an emulsifier was added after 3 hours from the addition of diisopropylbenzene hydroperoxide as an oxidant at an initial reaction step, and thereafter 1.5 wt. parts of rosin salt were added after 8 hours.
The polymerization temperature was initiated at 5xc2x0 C. and then, the temperature was increased from 5xc2x0 C. to 12xc2x0 C. after 3 hours. The initial reaction would be completed during that 3 hours. The temperature was also increased up to 20xc2x0 C. after 12-hour reaction and then, the reaction was further activated by increasing the temperature 25 xc2x0 C. after 4-hour reaction and terminated.
The general description of the obtained styrene-butadiene latex from the given recipe was shown in the following table 3.